1. Field of the Invention
The present invention relates to a method and apparatus for measuring a distortion coefficient, focal length or any other photographic parameter of a camera through a picture taken by the camera, and also relates to a computer storage medium for a computer program used to execute this method.
2. Description of the Prior Art
Hitherto, photographic parameters of a camera such as distortion coefficient and focal length have been measured by taking a point of known coordinates placed in a three-dimensional space and by observing the taken image. FIG. 1 (PRIOR ART) is a schematic diagram for showing a constitution of an apparatus for such conventional measuring method. In FIG. 1, symbol V represents a lattice point object, and plural lattice points of known two-dimensional coordinates are provided in the lattice point object V. Reference numeral 51 is a camera, which takes the lattice point object V plural times by varying the object distance, delivers the image data to an image display device 52 and a lattice point position extracting unit 53. The image display device 52 displays the image of the lattice point object V depending on the entered image data.
The lattice point position extracting unit 53 extracts the position on the image about the lattice point designated by user input from a pointing device 54, determines the image coordinates of the designated lattice point, and delivers same to a photographic parameter calculating unit 55. The photographic parameter calculating unit 55 calculates the photographic parameters of the camera 51 including the distortion parameter and focal length parameter, on the basis of the entered image coordinates of lattice point and distance to the camera 51 and the actual known three-dimensional coordinates of the lattice point, and delivers same to a photographic parameter outputting unit 56. The photographic parameter outputting unit 56 converts the calculated photographic parameters into character data or the like, and delivers same outside.
Recently, along with the advancement of the multimedia, processing images taken by camera is increasing. In this case, considering the photographic parameters of the camera used in taking the image, the image is processed by separating, combining or editing. Among the images to be processed, however, the kinds of cameras taking the images are often unknown and photographic conditions of the images are often unknown, that is, images of unknown photographic parameters of the camera used in taking pictures are included. In such a case, an image cannot be taken again by using a camera of unknown photographic conditions, and it is impossible to determine the photographic parameters of the camera by the conventional method. As a result, the image processing must be executed by using the image of unknown photographic parameters of the camera, and accurate image processing cannot be done.